Toward building the cow folliculome

One of the goals of the EmbryoGENE network was to gather information on the conditions leading to competent oocytes. Using a combination of transcriptomic analyses we are building the foundation of the folliculome, which will take the form of a virtual follicle with gene expression profiling data spanning small to ovulatory or atretic follicles. The different models currently being established not only provide information on the follicular conditions leading to good outcome but also intermediary steps, including evolution towards atresia. The physiology of very few species has been covered to the extent of our database, which is the only one for mono-ovulatory species. The first interesting observation extracted from our data is related to the plateau phase of follicular development, which is not a linear intermediate between growth and ovulation but rather an important modification step of tissue ontogenesis during which growth switches to differentiation or atresia. The markers of cell division, matrix rearrangement, mesenchymal differentiation, oxidation, steroidogenesis and ovulatory changes identified confirm known changes but also several others are now hinting to a more complex picture of this dynamic tissue. In addition to biomarkers, we have insight into the multiple pathways involved during the last few days before ovulation. Our new ability to validate these networks in vitro using primary granulosa cells culture also contributes to the construction of a follicular blueprint. The amazing list of gene responding to FSH alone is a good start but a complete meta-analysis will provide the foundation of the bovine folliculome.